class Solution {
public:
    int countSubstrings(string s) {
        int n = s.size();
        vector<vector<bool>> dp(n, vector<bool>(n));

        int count = 0;
        for (int i = n - 1; i >= 0; --i)
        {
            for (int j = i; j < n; ++j)
            {
                if (s[i] == s[j] && (i == j || i == j - 1 || dp[i + 1][j - 1]))
                {
                    dp[i][j] = true;
                    ++count;
                }
            }
        }
        return count;
    }
};